Similarly to the master armorer in The Witcher 3, you have to find your master blacksmith first before you can start the quest that allows you to unlock mastercrafted weapons. When you arrive in Novigrad, look for Hattori, the dumpling cook. Speaking with him will reveal that he’s actually a very skilled blacksmith who just needs the materials in order to forge some really cool looking swords. This will unlock the quest ‘Of Swords and Dumplings.’
Now, the recommended level for this quest is level 25, but you can attempt it at a level as low as level 15 as long as you’ve put in enough points into the Axii Sign. This will make things much easier for you as you won’t have to fight as many soldiers.
First, Hattori will ask you to meet him at the docks after nightfall to meet his supplier. When you meet up with them, bargain for 25% of the profits for both dialogue options and do not choose to stop the suppliers when they start to leave. If you stay silent and allow them to go, the suppliers will eventually give in and strike a deal with you. Following this, however, you and the suppliers will be ambushed by a group of dwarves. Don’t panic and let your fellow comrades absorb all the damage while you go in for safe hits.
After taking care of your enemies, visit Hattori at his shop. He will ask you to find him a bodyguard. Follow the quest marker on your map to find Sukrus. You’ll have to beat him in a fistfight before he’s willing to sit down and listen to what you’ve got to say. The fistfight isn’t too difficult as long as you take your time to parry and counter his strikes. After beating him, Sukrus will ask you to do him a favor.